Organic EL display device and electronic apparatus

ABSTRACT

Disclosed herein is an organic EL display device in which pixels each including an organic EL element formed by interposing an organic layer between an anode electrode and a cathode electrode are arranged in a matrix, the organic EL display device including: a common layer configured to be included in the organic EL element and be formed in the organic layer in common to the pixels; and a metal interconnect configured to surround periphery of the anode electrode and be electrically connected to the organic layer, wherein potential of the metal interconnect is set to a potential lower than potential of the anode electrode in a non-light-emission state of the organic EL element.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of U.S. patent application Ser. No.13/305,308, filed Nov. 28, 2011, now U.S. Pat. No. 8,581,275, to beissued Nov. 12, 2013, which in turn claims priority from JapaneseApplication No. 2011-013049, filed on Jan. 25, 2011, the entire contentsof which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to an organic EL display device andelectronic apparatus.

As one of planar type (flat panel type) display devices, there is adisplay device in which a so-called current-driven electroopticalelement whose light emission luminance changes depending on the value ofthe current flowing through the element is used as a light emitter(light emitting element) of the pixel. As the current-drivenelectrooptical element, an organic EL element is known. The organic ELelement utilizes electroluminescence (EL) of an organic material anduses a phenomenon in which an organic thin film emits light when anelectric field is applied thereto.

The organic EL display device using the organic EL element as the lightemitter of the pixel has the following features. Specifically, theorganic EL element has low power consumption because it can be driven byan applied voltage of 10 V or lower. The organic EL element is aself-luminous element and therefore provides high image visibilitycompared with a liquid crystal display device. In addition, the organicEL element easily allows reduction in the weight and thickness of thedisplay device because it does not require an illuminating componentsuch as a backlight. Moreover, the organic EL element has a very highresponse speed of several microseconds and therefore a residual image inmoving image displaying does not occur.

As the organic EL display device, a display device of a so-called RGBmask separate-application system obtained by separately applying organicEL materials of red (R), green (G), and blue (B) by evaporation with useof a mask is generally known. In contrast, there is a display devicethat is obtained without the RGB mask separate-application and is basedon a system in which the respective color light beams of RGB areobtained by the combination of an organic EL element that emits whitelight (hereinafter, referred to as “white organic EL element”) and acolor filter for the purpose of increase in the size and definition ofthe display device (refer to e.g. Japanese Patent Laid-open No.2003-123971).

SUMMARY

In the above-described organic EL display device based on thecombination of the white organic EL element and the color filter, acommon layer formed in common to the respective pixels exists. Theexistence of the common layer among the pixels causes the followingproblem. Specifically, leakage to a pixel that adjoins occurs throughthis common layer and the pixel that adjoins (hereinafter, referred toas “adjacent pixel”) also emits light slightly due to this leakage.Therefore, the color reproducibility (color purity) is deteriorated.

This problem is not limited to the organic EL display device based onthe combination of the white organic EL element and the color filter.Specifically, the same problem occurs also in e.g. an organic EL displaydevice of the mask separate-application system as long as a common layerexists among the pixels because leakage to the adjacent pixel occursthrough this common layer.

There is a need for a technique to provide an organic EL display devicecapable of eliminating the problem of leakage to the adjacent pixel toachieve favorable color reproducibility (color purity) and electronicapparatus having this organic EL display device.

According to one embodiment of the present disclosure, there is providedan organic EL display device in which pixels each including an organicEL element formed by interposing an organic layer between an anodeelectrode and a cathode electrode are arranged in a matrix. The organicEL display device includes a common layer configured to be included inthe organic EL element and be formed in the organic layer in common tothe pixels, and a metal interconnect configured to surround theperiphery of the anode electrode and be electrically connected to theorganic layer. The potential of the metal interconnect is set to apotential lower than the potential of the anode electrode in thenon-light-emission state of the organic EL element.

In the organic EL display device having the above-describedconfiguration, the metal interconnect electrically connected to theorganic layer is formed around the anode electrode. Due to this feature,even when a leakage current flows in the lateral direction through thecommon layer in the organic layer, this leakage current flows to themetal interconnect side. This can reduce the leakage current flowinginto an adjacent pixel and thus suppress light emission in the adjacentpixel.

According to the embodiment of the present disclosure, light emission inthe adjacent pixel can be suppressed even when a leakage current flowsin the lateral direction through the common layer in the organic layer.Thus, favorable color reproducibility (color purity) can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram showing the schematicconfiguration of an active-matrix organic EL display device to which oneembodiment of the present disclosure is applied;

FIG. 2 is a circuit diagram showing one example of the specific circuitconfiguration of a pixel (pixel circuit);

FIG. 3 is a timing waveform diagram for explaining the basic circuitoperation of the organic EL display device to which one embodiment ofthe present disclosure is applied;

FIGS. 4A to 4D are operation explanatory diagrams (first diagrams) ofthe basic circuit operation of the organic EL display device to whichone embodiment of the present disclosure is applied;

FIGS. 5A to 5D are operation explanatory diagrams (second diagrams) ofthe basic circuit operation of the organic EL display device to whichone embodiment of the present disclosure is applied;

FIGS. 6A and 6B are characteristic diagram FIG. 6A for explaining aproblem attributed to variation in the threshold voltage V_(th) of adrive transistor and a characteristic diagram FIG. 6B for explaining aproblem attributed to variation in the mobility μ of the drivetransistor;

FIG. 7 is a sectional view showing one example of a pixel structure of asystem of the combination of a white organic EL element and a colorfilter;

FIG. 8 is a sectional view of the major part showing one example of thestructure of a white organic EL element having a typical tandemstructure;

FIG. 9 is a circuit diagram showing the equivalent circuit of a displaypanel employing the system of the combination of the white organic ELelement and the color filter;

FIG. 10 is a sectional view of the major part showing one example of apixel structure including a white organic EL element having a tandemstructure according to an embodiment of the present disclosure;

FIG. 11 is a planar pattern diagram showing anode electrodes and theperiphery thereof;

FIG. 12 is an explanatory diagram about the operation and effect of theembodiment;

FIG. 13 is a circuit diagram showing the equivalent circuit of thedisplay panel having the pixel structure according to the embodiment;

FIG. 14 is a sectional view of the major part showing one example of apixel structure employing an RGB mask separate-application system;

FIG. 15 is a perspective view showing the appearance of a television setto which one embodiment of the present disclosure is applied;

FIGS. 16A and 16B are perspective views showing the appearance of adigital camera to which one embodiment of the present disclosure isapplied: FIG. 16A is a perspective view of the front side and FIG. 16Bis a perspective view of the back side;

FIG. 17 is a perspective view showing the appearance of a notebookpersonal computer to which one embodiment of the present disclosure isapplied;

FIG. 18 is a perspective view showing the appearance of a videocamcorder to which one embodiment of the present disclosure is applied;and

FIGS. 19A to 19G are appearance diagrams showing a cellular phone towhich one embodiment of the present disclosure is applied: FIG. 19A is afront view of the opened state, FIG. 19B is a side view of the openedstate, FIG. 19C is a front view of the closed state, FIG. 19D is a leftside view, FIG. 19E is a right side view, FIG. 19F is a top view, andFIG. 19G is a bottom view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A mode for carrying out the technique of the present disclosure(hereinafter, referred to as “embodiment”) will be described in detailbelow with reference to the drawings. The order of the description is asfollows.

1. Organic EL Display Device to Which Embodiment of Present DisclosureIs Applied

1-1. System Configuration

1-2. Basic Circuit Operation

1-3. System of Combination of White Organic EL Element and Color Filter

1-4. Problem of Leakage Current Due to Existence of Common Layer

2. Description of Embodiment

2-1. Pixel Structure to Reduce Leakage Current

2-2. Operation and Effect of Embodiment

3. Modification Example

4. Application Examples (Electronic Apparatus)

1. Organic EL Display Device to which Embodiment of Present Disclosureis Applied 1-1. System Configuration

FIG. 1 is a system configuration diagram showing the schematicconfiguration of an active-matrix organic EL display device to which oneembodiment of the present disclosure is applied.

The active-matrix organic EL display device is a display device thatcontrols the current flowing through an organic EL element, which is acurrent-driven electrooptical element, by an active element provided inthe same pixel as that of this organic EL element, e.g. aninsulated-gate field effect transistor. As the insulated-gate fieldeffect transistor, typically a thin film transistor (TFT) is used.

As shown in FIG. 1, an organic EL display device 10 according to thepresent application example has plural pixels 20 each including anorganic EL element, a pixel array section 30 in which these pixels 20are two-dimensionally arranged in a matrix, and a drive circuit sectiondisposed around this pixel array section 30. The drive circuit sectionis composed of a write scan circuit 40, a power supply scan circuit 50,a signal output circuit 60, and so forth and drives the respectivepixels 20 of the pixel array section 30.

If the organic EL display device 10 is for color displaying, one pixelserving as the unit to form a color image (unit pixel) is composed ofplural sub-pixels and each of the sub-pixels is equivalent to the pixel20 in FIG. 1. Specifically, in the display device for color displaying,one pixel is composed of e.g. three sub-pixels, a sub-pixel to emit red(R) light, a sub-pixel to emit green (G) light, and a sub-pixel to emitblue (B) light.

However, the configuration of one pixel is not limited to thecombination of sub-pixels of three primary colors of RGB and it is alsopossible to configure one pixel by further adding a sub-pixel of onecolor or plural colors to the sub-pixels of three primary colors.Specifically, for example it is also possible to configure one pixel byadding a sub-pixel to emit white (W) light for luminance enhancement andto configure one pixel by adding at least one sub-pixel to emitcomplementary-color light for widening of the color reproduction range.

In the pixel array section 30, for the arrangement of the pixels 20 on mrows and n columns, scan lines 31 ₁ to 31 _(m) and power supply lines 32₁ to 32 _(m) are wired along the row direction (arrangement direction ofthe pixels on the pixel row) on each pixel row basis. Furthermore, forthe arrangement of the pixels 20 on m rows and n columns, signal lines33 ₁ to 33 _(n) are wired along the column direction (arrangementdirection of the pixels on the pixel column) on each pixel column basis.

Each of the scan lines 31 ₁ to 31 _(m) is connected to the outputterminal of the write scan circuit 40 for the corresponding row. Each ofthe power supply lines 32 ₁ to 32 _(m) is connected to the outputterminal of the power supply scan circuit 50 for the corresponding row.Each of the signal lines 33 ₁ to 33 _(n) is connected to the outputterminal of the signal output circuit 60 for the corresponding column.

The pixel array section 30 is normally formed on a transparentinsulating substrate such as a glass substrate. Thus, the organic ELdisplay device 10 has a planar type (flat type) panel structure. Thedrive circuits of the respective pixels 20 of the pixel array section 30can be formed by using an amorphous silicon TFT or a low-temperaturepoly-silicon TFT. If a low-temperature poly-silicon TFT is used, thewrite scan circuit 40, the power supply scan circuit 50, and the signaloutput circuit 60 can also be mounted on a display panel (substrate) 70,which forms the pixel array section 30, as shown in FIG. 1.

The write scan circuit 40 is configured with a shift register circuitthat sequentially shifts (transfers) a start pulse sp in synchronizationwith a clock pulse ck, and so forth. In writing of the signal voltage ofa video signal to the respective pixels 20 of the pixel array section30, this write scan circuit 40 sequentially supplies a write scan signalWS (WS₁ to WS_(m)) to the scan line 31 (31 ₁ to 31 _(m)) to thereby scanthe respective pixels 20 of the pixel array section 30 in turn on arow-by-row basis (line-sequential scanning).

The power supply scan circuit 50 is configured with a shift registercircuit that sequentially shifts the start pulse sp in synchronizationwith the clock pulse ck, and so forth. This power supply scan circuit 50supplies, to the power supply line 32 (32 ₁ to 32 _(m)), a supplypotential DS (DS₁ to DS_(m)) capable of being switched between a firstsupply potential V_(ccp) and a second supply potential V_(ini) lowerthan the first supply potential V_(ccp) in synchronization with theline-sequential scanning by the write scan circuit 40. As describedlater, light-emission/non-light-emission of the pixel 20 is controlledby the switching of V_(ccp)/V_(ini) of the supply potential DS.

The signal output circuit 60 selectively outputs a reference voltageV_(ofs) and a signal voltage V_(sig) of the video signal correspondingto luminance information supplied from a signal supply source (notshown) (hereinafter, it will be often referred to simply as “signalvoltage”). The reference voltage V_(ofs) is the potential serving as thebasis of the signal voltage V_(sig) of the video signal (e.g. potentialequivalent to the black level of the video signal) and is used inthreshold correction processing to be described later.

The signal voltage V_(sig)/reference voltage V_(ofs) output from thesignal output circuit 60 is written to the respective pixels 20 of thepixel array section 30 via the signal line 33 (33 ₁ to 33 _(n)) in unitsof the pixel row selected by scanning by the write scan circuit 40. Thatis, the signal output circuit 60 employs the driving form ofline-sequential writing to write the signal voltage V_(sig) in units ofthe row (line).

(Pixel Circuit)

FIG. 2 is a circuit diagram showing one example of the specific circuitconfiguration of the pixel (pixel circuit) 20. The light emitter of thepixel 20 is formed of an organic EL element 21, which is acurrent-driven electrooptical element whose light emission luminancechanges depending on the value of the current flowing through theelement.

As shown in FIG. 2, the pixel 20 is configured with the organic ELelement 21 and the drive circuit that drives the organic EL element 21by applying a current to the organic EL element 21. The cathodeelectrode of the organic EL element 21 is connected to a common powersupply line 34 wired in common to all pixels 20 (so-called blanketinterconnect).

The drive circuit to drive the organic EL element 21 has a drivetransistor 22, a write transistor 23, hold capacitance 24, and auxiliarycapacitance 25. N-channel TFTs can be used as the drive transistor 22and the write transistor 23. However, this combination of theconductivity type of the drive transistor 22 and the write transistor 23is merely one example and the combination of the conductivity type isnot limited thereto.

One electrode (source/drain electrode) of the drive transistor 22 isconnected to the power supply line 32 (32 ₁ to 32 _(m)) and the otherelectrode (drain/source electrode) is connected to the anode electrodeof the organic EL element 21.

One electrode (source/drain electrode) of the write transistor 23 isconnected to the signal line 33 (33 ₁ to 33 _(n)) and the otherelectrode (drain/source electrode) is connected to the gate electrode ofthe drive transistor 22. The gate electrode of the write transistor 23is connected to the scan line 31 (31 ₁ to 31 _(m)).

In the drive transistor 22 and the write transistor 23, one electroderefers to the metal interconnect electrically connected to thesource/drain region and the other electrode refers to the metalinterconnect electrically connected to the drain/source region.Depending on the potential relationship between one electrode and theother electrode, possibly one electrode serves as either the sourceelectrode or the drain electrode and the other electrode serves aseither the drain electrode or the source electrode.

One electrode of the hold capacitance 24 is connected to the gateelectrode of the drive transistor 22 and the other electrode isconnected to the other electrode of the drive transistor 22 and theanode electrode of the organic EL element 21.

One electrode of the auxiliary capacitance 25 is connected to the anodeelectrode of the organic EL element 21 and the other electrode isconnected to the common power supply line 34. This auxiliary capacitance25 is provided according to need in order to compensate forinsufficiency of the capacitance of the organic EL element 21 andenhance the gain of writing of the video signal to the hold capacitance24. That is, the auxiliary capacitance 25 is not an essentialconstituent element and can be omitted if the equivalent capacitance ofthe organic EL element 21 is sufficiently high.

In this example, the other electrode of the auxiliary capacitance 25 isconnected to the common power supply line 34. However, the connectionsubject of the other electrode is not limited to the common power supplyline 34 as long as the connection subject is a node at a fixedpotential. Connecting the other electrode of the auxiliary capacitance25 to the node of a fixed potential allows achievement of the desiredpurposes of compensating for insufficiency of the capacitance of theorganic EL element 21 and enhancing the gain of writing of the videosignal to the hold capacitance 24.

In the pixel 20 having the above-described configuration, the writetransistor 23 becomes the conductive state in response to theHigh-active write scan signal WS applied from the write scan circuit 40to the gate electrode via the scan line 31. Thereby, the writetransistor 23 performs sampling of the signal voltage V_(sig) of thevideo signal corresponding to luminance information or the referencevoltage V_(ofs), supplied from the signal output circuit 60 via thesignal line 33, and writes it in the pixel 20. This written signalvoltage V_(sig) or reference voltage V_(ofs) is applied to the gateelectrode of the drive transistor 22 and held in the hold capacitance24.

When the supply potential DS of the power supply line 32 (32 ₁ to 32_(m)) is the first supply potential V_(ccp), one electrode of the drivetransistor 22 serves as the drain electrode and the other electrodeserves as the source electrode and the drive transistor 22 operates inthe saturation region. Thereby, the drive transistor 22 receives supplyof a current from the power supply line 32 and drives light emission ofthe organic EL element 21 based on current driving. Specifically, thedrive transistor 22 operates in the saturation region to thereby supply,to the organic EL element 21, a drive current having the current valuedepending on the voltage value of the signal voltage V_(sig) held in thehold capacitance 24 and make the organic EL element 21 emit light bycurrent driving thereof.

When the supply potential DS is switched from the first supply potentialV_(ccp) to the second supply potential V_(ini), one electrode of thedrive transistor 22 serves as the source electrode and the otherelectrode serves as the drain electrode and the drive transistor 22operates as a switching transistor. Thereby, the drive transistor 22stops the supply of the drive current to the organic EL element 21 andturns the organic EL element 21 to the non-light-emission state. Thatis, the drive transistor 22 has also a function as a transistor tocontrol light-emission/non-light-emission of the organic EL element 21.

This switching operation of the drive transistor 22 can set the periodduring which the organic EL element 21 is in the non-light-emissionstate (non-light-emission period) and control the ratio between thelight-emission period and the non-light-emission period of the organicEL element 21 (duty). By this duty control, the residual image bluraccompanying the light emission of the pixel over one display frameperiod can be reduced and thus particularly the image quality of movingimages can be made more excellent.

Of the first and second supply potentials V_(ccp) and V_(ini)selectively supplied from the power supply scan circuit 50 via the powersupply line 32, the first supply potential V_(ccp) is a supply potentialfor supplying the drive current for light emission driving of theorganic EL element 21 to the drive transistor 22. The second supplypotential V_(ini) is a supply potential for applying a reverse bias tothe organic EL element 21. This second supply potential V_(ini) is setto a potential lower than the reference voltage V_(ofs), e.g. apotential lower than V_(ofs)−V_(th) when the threshold voltage of thedrive transistor 22 is V_(th), preferably to a potential sufficientlylower than V_(ofs)−V_(th).

1-2. Basic Circuit Operation

The basic circuit operation of the organic EL display device 10 havingthe above-described configuration will be described below based on atiming waveform diagram of FIG. 3 with use of operation explanatorydiagrams of FIGS. 4A to 5D. In the operation explanatory diagrams ofFIGS. 4A to 5D, the write transistor 23 is shown by a switch symbol forsimplification of the drawings. Furthermore, the auxiliary capacitance25 of the organic EL element 21 is also shown.

The timing waveform diagram of FIG. 3 shows change in each of thepotential (write scan signal) WS of the scan line 31, the potential(supply potential) DS of the power supply line 32, the potential(V_(sig)/V_(ofs)) of the signal line 33, and the gate potential V_(g)and the source potential V_(s) of the drive transistor 22.

(Light-Emission Period of Previous Display Frame)

In the timing waveform diagram of FIG. 3, the period before a time t₁₁is the light-emission period of the organic EL element 21 in theprevious display frame. In this light-emission period of the previousdisplay frame, the potential DS of the power supply line 32 is the firstsupply potential (hereinafter, referred to as “higher potential”)V_(ccp) and the write transistor 23 is in the non-conductive state.

The drive transistor 22 is so designed as to operate in the saturationregion at this time. Thus, as shown in FIG. 4A, the drive current(drain-source current) I_(ds) depending on the gate-source voltageV_(gs) of the drive transistor 22 is supplied from the power supply line32 to the organic EL element 21 via the drive transistor 22. Therefore,the organic EL element 21 emits light with the luminance depending onthe current value of the drive current I_(ds).

(Threshold Correction Preparation Period)

At the time t₁₁, a new display frame (present display frame) of theline-sequential scanning starts. At this time, as shown in FIG. 4B, thepotential DS of the power supply line 32 is switched from the higherpotential V_(ccp) to the second supply potential (hereinafter, referredto as “lower potential”) V_(ini) sufficiently lower than V_(ofs)−V_(th)with respect to the reference voltage V_(ofs) of the signal line 33.

Here, the threshold voltage of the organic EL element 21 is defined asV_(thel) and the potential of the common power supply line 34 (cathodepotential) is defined as V_(cath). If the lower potential V_(ini) is soset as to satisfy a relationship of V_(ini)<V_(thel)+V_(cath), theorganic EL element 21 becomes the reverse-biased state and stops itslight emission because the source potential V_(s) of the drivetransistor 22 becomes almost equal to the lower potential V_(ini).

Next, the potential WS of the scan line 31 is shifted from thelower-potential side to the higher-potential side at a time t₁₂.Thereby, the write transistor 23 becomes the conductive state as shownin FIG. 4C. At this time, the reference voltage V_(ofs) is supplied fromthe signal output circuit 60 to the signal line 33 and therefore thegate potential V_(g) of the drive transistor 22 becomes the referencevoltage V_(ofs). The source potential V_(s) of the drive transistor 22is a potential sufficiently lower than the reference voltage V_(ofs),i.e. the lower potential V_(ini).

At this time, the gate-source voltage V_(gs) of the drive transistor 22is V_(ofs)−V_(ini). Unless V_(ofs)−V_(ini) is higher than the thresholdvoltage V_(th) of the drive transistor 22, the threshold correctionprocessing to be described later cannot be executed. Therefore, apotential relationship of V_(ofs)−V_(ini)>V_(th) should be set.

This processing of initializing the potentials by fixing the gatepotential V_(g) of the drive transistor 22 to the reference voltageV_(ofs) and fixing (settling) the source potential V_(s) to the lowerpotential V_(ini) in this manner is preparation (threshold correctionpreparation) processing preceding the threshold correction processing(threshold correction operation) to be described later. Therefore, thereference voltage V_(ofs) and the lower potential V_(ini) serve as theinitialization potential for the gate potential V_(g) and the sourcepotential V_(s), respectively, of the drive transistor 22.

(Threshold Correction Period)

Next, at a time t₁₃, the potential DS of the power supply line 32 isswitched from the lower potential V_(ini) to the higher potentialV_(ccp) as shown in FIG. 4D. Thereupon, the threshold correctionprocessing is started, with the gate potential V_(g) of the drivetransistor 22 kept at the reference voltage V_(ofs). Specifically, thesource potential V_(s) of the drive transistor 22 starts to rise towardthe potential obtained by subtracting the threshold voltage V_(th) ofthe drive transistor 22 from the gate potential V_(g).

Here, for convenience, the processing in which the initializationpotential V_(ofs) for the gate potential V_(g) of the drive transistor22 is used as the basis and the source potential V_(s) is changed towardthe potential obtained by subtracting the threshold voltage V_(th) ofthe drive transistor 22 from this initialization potential V_(ofs) iscalled the threshold correction processing. Along with the progressionof this threshold correction processing, the gate-source voltage V_(gs)of the drive transistor 22 converges on the threshold voltage V_(th) ofthe drive transistor 22 in due course. The voltage equivalent to thisthreshold voltage V_(th) is held in the hold capacitance 24.

In order that the current may flow exclusively to the hold capacitance24 and be prevented from flowing to the organic EL element 21 in theperiod of the threshold correction processing (threshold correctionperiod), the potential V_(cath) of the common power supply line 34 is soset that the organic EL element 21 is kept at the cut-off state in thisperiod.

Next, the potential WS of the scan line 31 is shifted to thelower-potential side at a time t₁₄. Thereby, the write transistor 23becomes the non-conductive state as shown in FIG. 5A. At this time, thegate electrode of the drive transistor 22 is electrically isolated fromthe signal line 33 to thereby become the floating state. However,because the gate-source voltage V_(gs) is equal to the threshold voltageV_(th) of the drive transistor 22, the drive transistor 22 is in thecut-off state. Therefore, the drain-source current I_(ds) does not flowthrough the drive transistor 22.

(Signal Writing and Mobility Correction Period)

Next, at a time t₁₅, the potential of the signal line 33 is switchedfrom the reference voltage V_(ofs) to the signal voltage V_(sig) of thevideo signal as shown in FIG. 5B. Subsequently, at a time t₁₆, thepotential WS of the scan line 31 is shifted to the higher-potentialside. Thereby, as shown in FIG. 5C, the write transistor 23 becomes theconductive state to perform sampling of the signal voltage V_(sig) ofthe video signal and write it in the pixel 20.

Due to this writing of the signal voltage V_(sig) by the writetransistor 23, the gate potential V_(g) of the drive transistor 22becomes the signal voltage V_(sig). In driving of the drive transistor22 based on the signal voltage V_(sig) of the video signal, thethreshold voltage V_(th) of the drive transistor 22 is canceled out bythe voltage equivalent to the threshold voltage V_(th) held in the holdcapacitance 24. Details of the principle of this threshold cancel willbe described later.

At this time, the organic EL element 21 is in the cut-off state(high-impedance state). Therefore, the current (drain-source currentI_(ds)) flowing from the power supply line 32 to the drive transistor 22depending on the signal voltage V_(sig) of the video signal flows intothe equivalent capacitance of the organic EL element 21 and theauxiliary capacitance 25. Thereby, the charge of the equivalentcapacitance of the organic EL element 21 and the auxiliary capacitance25 is started.

Due to the charge of the equivalent capacitance of the organic ELelement 21 and the auxiliary capacitance 25, the source potential V_(s)of the drive transistor 22 rises over time. At this time, variation inthe threshold voltage V_(th) of the drive transistor 22 from pixel topixel has been already canceled and the drain-source current I_(ds) ofthe drive transistor 22 depends on the mobility μ of the drivetransistor 22. The mobility μ of the drive transistor 22 is the mobilityof the semiconductor thin film configuring the channel of the drivetransistor 22.

Here, suppose that the ratio of the held voltage V_(gs) of the holdcapacitance 24 to the signal voltage V_(sig) of the video signal, i.e. awriting gain G, is one (ideal value). In this case, due to the rise ofthe source potential V_(s) of the drive transistor 22 to a potential ofV_(ofs)−V_(th)+ΔV, the gate-source voltage V_(gs) of the drivetransistor 22 becomes V_(sig)−V_(ofs)+V_(th)−ΔV.

Specifically, the rise component ΔV of the source potential V_(s) of thedrive transistor 22 acts in such a manner as to be subtracted from thevoltage (V_(sig)−V_(ofs)+V_(th)) held in the hold capacitance 24, i.e.as to discharge the charge accumulated in the hold capacitance 24. Inother words, the rise component ΔV of the source potential V_(s) meansnegative feedback to the hold capacitance 24. Therefore, the risecomponent ΔV of the source potential V_(s) is equivalent to the feedbackamount of the negative feedback.

By applying negative feedback to the gate-source voltage V_(gs) with thefeedback amount ΔV depending on the drain-source current I_(ds) flowingthrough the drive transistor 22 in this manner, the dependence of thedrain-source current I_(ds) of the drive transistor 22 on the mobility μcan be canceled. This cancel processing is the mobility correctionprocessing to correct variation in the mobility μ of the drivetransistor 22 from pixel to pixel.

Specifically, when the signal amplitude V_(in) (=V_(sig)−V_(ofs)) of thevideo signal written to the gate electrode of the drive transistor 22 ishigher, the drain-source current I_(ds) is larger and thus the absolutevalue of the feedback amount ΔV of the negative feedback is also larger.Therefore, the mobility correction processing depending on the lightemission luminance level is executed.

If the signal amplitude V_(in) of the video signal is set constant, whenthe mobility μ of the drive transistor 22 is higher, the absolute valueof the feedback amount ΔV of the negative feedback is also larger. Thus,variation in the mobility μ from pixel to pixel can be eliminated.Therefore, the feedback amount ΔV of the negative feedback can beregarded also as the correction amount of the mobility correctionprocessing. Details of the principle of the mobility correction will bedescribed later.

(Light-Emission Period)

Next, the potential WS of the scan line 31 is shifted to thelower-potential side at a time t₁₇. Thereby, the write transistor 23becomes the non-conductive state as shown in FIG. 5D. Thus, the gateelectrode of the drive transistor 22 is electrically isolated from thesignal line 33 and therefore becomes the floating state.

When the gate electrode of the drive transistor 22 is in the floatingstate, the gate potential V_(g) also changes in conjunction with changein the source potential V_(s) of the drive transistor 22 because thehold capacitance 24 is connected between the gate and source of thedrive transistor 22. The operation of this change in the gate potentialV_(g) of the drive transistor 22 in conjunction with the change in thesource potential V_(s) is bootstrap operation by the hold capacitance24.

The gate electrode of the drive transistor 22 becomes the floating stateand simultaneously the drain-source current I_(ds) of the drivetransistor 22 starts to flow to the organic EL element 21. Thereby, theanode potential of the organic EL element 21 rises depending on thiscurrent I_(ds).

When the anode potential of the organic EL element 21 surpassesV_(thel)+V_(cath), the drive current starts to flow to the organic ELelement 21 and thus the organic EL element 21 starts light emission. Therise of the anode potential of the organic EL element 21 is nothing moreor less than the rise of the source potential V_(s) of the drivetransistor 22. When the source potential V_(s) of the drive transistor22 rises, the gate potential V_(g) of the drive transistor 22 also risesin conjunction with this source potential rise due to the bootstrapoperation of the hold capacitance 24.

At this time, the amount of rise of the gate potential V_(g) is equal tothat of rise of the source potential V_(s) if it is assumed that thebootstrap gain is one (ideal value). Therefore, during thelight-emission period, the gate-source voltage V_(gs) of the drivetransistor 22 is kept constant at V_(sig)−V_(ofs)+V_(th)−ΔV. At a timet₁₈, the potential of the signal line 33 is switched from the signalvoltage V_(sig) of the video signal to the reference voltage V_(ofs).

In the above-described series of circuit operation, the respectiveprocessing operations of the threshold correction preparation, thethreshold correction, the writing of the signal voltage V_(sig) (signalwriting), and the mobility correction are carried out in one horizontalscanning period (1H). Furthermore, the respective processing operationsof the signal writing and the mobility correction are carried out inparallel in the period from the time t₁₆ to the time t₁₇.

[Divided Threshold Correction]

The above description is made by taking as an example the case ofemploying the driving method in which the threshold correctionprocessing is executed only once. However, this driving method is merelyone example and the driving method is not limited thereto. For example,it is also possible to employ a driving method in which so-calleddivided threshold correction is performed, i.e. the threshold correctionprocessing is executed plural times in a divided manner over pluralhorizontal scanning periods preceding the 1H period in which thethreshold correction processing is executed together with the mobilitycorrection and signal writing processing in addition to this 1H period.

If this driving method with the divided threshold correction isemployed, a sufficient time can be ensured as the threshold correctionperiod over plural horizontal scanning periods even if the timeallocated as one horizontal scanning period becomes short due toincrease in the number of pixels in association with enhancement in thedefinition. Therefore, even if the time allocated as one horizontalscanning period becomes short, the threshold correction processing canbe surely executed because a sufficient time can be ensured as thethreshold correction period.

[Principle of Threshold Cancel]

The principle of the threshold cancel (i.e. threshold correction) forthe drive transistor 22 will be described below. The drive transistor 22is so designed as to operate in the saturation region and thereforeoperates as a constant current source. Thus, the constant drain-sourcecurrent (drive current) I_(ds) given by the following equation (1) issupplied from the drive transistor 22 to the organic EL element 21.I _(ds)=(½)·μ(W/L)C _(ox)(V _(gs) −V _(th))²  (1)

In this equation, W is the channel width of the drive transistor 22. Lis the channel length. C_(ox) is the gate capacitance per unit area.

FIG. 6A shows the characteristic of drain-source current I_(ds) vs.gate-source voltage V_(gs) of the drive transistor 22. As shown in thecharacteristic diagram of FIG. 6A, unless the cancel processing(correction processing) for variation in the threshold voltage V_(th) ofthe drive transistor 22 from pixel to pixel is executed, thedrain-source current I_(ds) corresponding to the gate-source voltageV_(gs) is I_(ds1) when the threshold voltage V_(th) is V_(th1).

On the other hand, when the threshold voltage V_(th) is V_(th2)(V_(th2)>V_(th1)), the drain-source current I_(ds) corresponding to thesame gate-source voltage V_(gs) is I_(ds2) (I_(ds2)<I_(ds1)). That is,if the threshold voltage V_(th) of the drive transistor 22 varies, thedrain-source current I_(ds) varies even when the gate-source voltageV_(gs) is constant.

In the pixel (pixel circuit) 20 having the above-describedconfiguration, the gate-source voltage V_(gs) of the drive transistor 22in light emission is V_(sig)−V_(ofs)+V_(th)−ΔV as described above.Therefore, if this voltage V_(gs) is substituted in equation (1), thedrain-source current I_(ds) is represented by the following equation(2).I _(ds)=(½)·μ(W/L)C _(ox)(V _(sig) −V _(ofs) −ΔV)²  (2)

That is, the term of the threshold voltage V_(th) of the drivetransistor 22 is canceled, so that the drain-source current I_(ds)supplied from the drive transistor 22 to the organic EL element 21 doesnot depend on the threshold voltage V_(th) of the drive transistor 22.As a result, even when the threshold voltage V_(th) of the drivetransistor 22 varies from pixel to pixel due to variation in themanufacturing process of the drive transistor 22, change over time, andso forth, the drain-source current I_(ds) does not vary and thus thelight emission luminance of the organic EL element 21 can be keptconstant.

[Principle of Mobility Correction]

The principle of the mobility correction for the drive transistor 22will be described below. FIG. 6B shows characteristic curves withcomparison between pixel A in which the mobility μ of the drivetransistor 22 is relatively higher and pixel B in which the mobility μof the drive transistor 22 is relatively lower. If the drive transistor22 is configured by a poly-silicon thin film transistor or the like,inevitably the mobility μ varies among the pixels like pixel A and pixelB.

A consideration will be made below about the case in which the mobilityμ varies between pixels A and B and e.g. the signal amplitude V_(in)(=V_(sig)−V_(ofs)) at the same level is written to the gate electrode ofthe drive transistor 22 of both pixels A and B. In this case, ifcorrection of the mobility μ is not performed at all, large differencearises between a drain-source current I_(ds1)′ flowing in pixel A havingthe higher mobility μ and a drain-source current I_(ds2)′ flowing inpixel B having the lower mobility μ. If large difference in thedrain-source current I_(ds) arises among the pixels attributed tovariation in the mobility μ among the pixels in this manner, theuniformity (evenness) of the screen is spoiled.

As is apparent from the transistor characteristic expression of theabove-described equation (1), the higher mobility μ yields the largerdrain-source current I_(ds). Therefore, the higher the mobility μ is,the larger the feedback amount ΔV of negative feedback is. As shown inFIG. 6B, a feedback amount ΔV₁ in pixel A having the higher mobility μis larger than a feedback amount ΔV₂ in pixel B having the lowermobility μ.

So, if negative feedback is applied to the gate-source voltage V_(gs)with the feedback amount ΔV depending on the drain-source current I_(ds)of the drive transistor 22 by the mobility correction processing, theextent of this negative feedback is larger when the mobility μ ishigher. As a result, the variation in the mobility μ from pixel to pixelcan be suppressed.

Specifically, when correction with the feedback amount ΔV₁ is performedin pixel A having the higher mobility μ, the drain-source current I_(ds)greatly drops from I_(ds1)′ to I_(ds1). In contrast, the feedback amountΔV₂ in pixel B having the lower mobility μ is small. Therefore, thedrain-source current I_(ds) does not drop so greatly, i.e. the drop isfrom I_(ds2)′ to I_(ds2). As a result, the drain-source current I_(ds1)of pixel A is almost equal to the drain-source current I_(ds2) of pixelB, so that the variation in the mobility μ from pixel to pixel iscorrected.

In conclusion, when there are pixel A and pixel B having the differentmobility μ, the feedback amount ΔV₁ in pixel A having the highermobility μ is larger than the feedback amount ΔV₂ in pixel B having thelower mobility μ. That is, the feedback amount ΔV is larger and theamount of decrease in the drain-source current I_(ds) is larger in thepixel having the higher mobility μ.

Therefore, by applying negative feedback to the gate-source voltageV_(gs) with the feedback amount ΔV depending on the drain-source currentI_(ds) of the drive transistor 22, the current value of the drain-sourcecurrent I_(ds) of the pixels having the different mobility μ is madeuniform. As a result, variation in the mobility μ from pixel to pixelcan be corrected. That is, the mobility correction processing is theprocessing of applying negative feedback to the gate-source voltageV_(gs) of the drive transistor 22, i.e. the hold capacitance 24, withthe feedback amount (correction amount) ΔV depending on the current(drain-source current I_(ds)) flowing through the drive transistor 22.

1-3. System of Combination of White Organic EL Element and Color Filter

In the organic EL display device 10 according to the above-describedpresent application example, the RGB mask separate-application system isnot employed and a system in which the respective color light beams ofRGB are obtained by the combination of a white organic EL element 21_(W) and a color filter 80 as shown in FIG. 7 is employed. The RGB maskseparate-application system is a system in which organic EL materials ofRGB are separately applied by evaporation with use of a mask. The systemof the combination of the white organic EL element 21 _(W) and the colorfilter 80 is suitable for increase in the size and definition of thedisplay panel 70.

(White Organic EL Element Having Tandem Structure)

As the white organic EL element 21 _(W), an organic EL element having atandem structure is widely known. For example, the tandem structure isformed by coupling (stacking) plural units (light emitting units) of anorganic layer including the respective light emitting layers of RGB in aseries (tandem) manner with the intermediary of connecting layers. Fromthe white organic EL element having this tandem structure, white lightis obtained through superposition of the light emission of therespective light emitting units of RGB.

FIG. 8 is a sectional view of the major part showing one example of thestructure of the white organic EL element having a typical tandemstructure. Here, a three-stage tandem structure is taken as one exampleand a basic structure is shown in a simplified manner for simplificationof the diagram. Furthermore, FIG. 8 shows the pixel structure of twosub-pixels of RG among three sub-pixels of RGB.

Referring to FIG. 8, anode electrodes 211 (211 _(R), 211 _(G), 211 _(B))are provided on a pixel-by-pixel basis at the bottom of a recess 71 _(A)of a window insulating film 71. An organic layer 213 is provided incommon to all pixels between the anode electrodes 211 and a cathodeelectrode 212 provided in common to all pixels, so that the whiteorganic EL element 21 _(W) is configured. An interlayer insulating film72 is stacked on the cathode electrode 212 and the color filter 80 isformed on this interlayer insulating film 72 in an on-chip form (on-chipcolor filter).

In the white organic EL element 21 _(W), the organic layer 213 is formedby sequentially depositing a charge injection layer 214, a lightemitting layer 215 _(R) of R, a connecting layer 216, a light emittinglayer 215 _(G) of G, a connecting layer 217, and a light emitting layer215 _(B) of B over the anode electrodes 211 in common to all pixels, asone example. Under current driving by the drive transistor 22 in FIG. 2,a current flows from the drive transistor 22 to the organic layer 213via the anode electrode 211. Thereby, recombination of electrons andholes occurs in the respective light emitting layers 215 _(R), 215 _(G),and 215 _(B) in the organic layer 213. In this recombination, lightemission occurs.

At this time, the light emission colors of the respective light emittinglayers 215 _(R), 215 _(G), and 215 _(B) of R, G, and B are superimposedon (combined with) each other to become white light. The white lightemitted from the white organic EL element 21 _(W) on a pixel-by-pixelbasis is transmitted through the color filter 80. By combining the whiteorganic EL element 21 _(W) with the color filter 80 in this manner, therespective color light beams of R, G, and B can be obtained from thewhite light.

1-4. Problem of Leakage Current Due to Existence of Common Layer

In the organic EL display device 10 formed by disposing the pixels(sub-pixels) including the white organic EL element 21 _(W) having theabove-described tandem structure, a common layer formed in common to therespective pixels exists. Specifically, as is apparent from FIG. 8particularly, the charge injection layer 214, the connecting layer 216,and the connecting layer 217 are the common layers formed in common tothe respective pixels.

A consideration will be made about a problem of leakage current due tothe existence of the common layer (leakage current flowing through thecommon layer) by taking as an example the case in which only the pixel(sub-pixel) of R emits light in FIG. 8. FIG. 9 shows the equivalentcircuit of the display panel 70 in the case of employing the system ofthe combination of the white organic EL element 21 _(W) and the colorfilter 80.

In the display panel 70 employing the system of the combination of thewhite organic EL element 21 _(W) and the color filter 80, leakage in thelateral direction occurs in layers (common layers) havingcomparatively-low impedance, such as the charge injection layer 214 andthe connecting layers 216 and 217. The lateral direction refers to theflow direction of the leakage current when the flow direction of thecurrent flowing in the white organic EL element 21 _(W) is defined asthe vertical direction. Due to this leakage current, an area outside theanode electrode 211 also emits light.

No problem is caused if the distance between adjacent pixels issufficiently long (separate). However, if the distance between adjacentpixels is short and the leakage current flows into the adjacent pixel,the area of light emission accompanying the leakage current ranges tothe adjacent pixel. As a result, the adjacent pixel also emits light. InFIG. 8, the size of the arrow representing the light emission colorconceptually indicates the intensity of this light. In the case of thepresent example, the pixel of G adjacent to the pixel of R that shouldemit light originally also emits light. This deteriorates the colorreproducibility (color purity). Although the light emitting layers 215_(R), 215 _(G), and 215 _(B) are also common layers, generally they arefree from the problem of the leakage because the impedance thereof ishigh compared with the charge injection layer 214, the connecting layers216 and 217, and so forth.

2. Description of Embodiment

In the present embodiment, in order to solve the problem of the leakagecurrent due to the existence of the common layer in an organic ELdisplay device including at least one common layer formed in an organiclayer in common to the pixels, a metal interconnect electricallyconnected to the organic layer is so formed as to surround the peripheryof the anode electrode. Furthermore, the present embodiment employs aconfiguration in which the potential of this metal interconnect is setto a potential lower than the potential of the anode electrode in thenon-light-emission state of the organic EL element.

Due to the characteristic that the metal interconnect electricallyconnected to the organic layer is formed around the anode electrode,even when a leakage current flows in the lateral direction through thecommon layer in the organic layer, this leakage current flows to themetal interconnect side. This can reduce the leakage current flowinginto the adjacent pixel and thus can suppress light emission in theadjacent pixel. As a result, favorable color reproducibility (colorpurity) can be achieved.

2-1. Pixel Structure to Reduce Leakage Current

A pixel structure to reduce the leakage current flowing through thecommon layer in the organic layer will be specifically described below.

FIG. 10 is a sectional view of the major part showing one example of thepixel structure including a white organic EL element having a tandemstructure according to the embodiment. In FIG. 10, the part equivalentto that in FIG. 8 is given the same numeral. FIG. 11 shows a planarpattern diagram of the anode electrodes and the periphery thereof. Here,a three-stage tandem structure is taken as one example and a basicstructure is shown in a simplified manner for simplification of thediagram. Furthermore, FIG. 10 shows the pixel structure of twosub-pixels of RG among three sub-pixels of RGB.

Regarding the basic structure, the white organic EL element having thetandem structure according to the present embodiment is the same as theabove-described white organic EL element having the typical tandemstructure. Specifically, as shown in FIG. 10, the anode electrodes 211(211 _(R), 211 _(G), 211 _(B)) are provided on a pixel-by-pixel basis atthe bottom of the recess 71 _(A) of the window insulating film 71. Theorganic layer 213 is provided in common to all pixels between the anodeelectrodes 211 and the cathode electrode 212 provided in common to allpixels, so that the white organic EL element 21 _(W) is configured.

In the white organic EL element 21 _(W), the organic layer 213 is formedby sequentially depositing the charge injection layer 214, the lightemitting layer 215 _(R) of R, the connecting layer 216, the lightemitting layer 215 _(G) of G, the connecting layer 217, and the lightemitting layer 215 _(B) of B over the anode electrodes 211 in common toall pixels, as one example. The interlayer insulating film 72 is stackedon the cathode electrode 212 and the color filter 80 is formed on thisinterlayer insulating film 72 in an on-chip form.

In the pixel structure including the white organic EL element 21 _(W)having the tandem structure with the above-described configuration, thepresent embodiment has the following features. First, a metalinterconnect 90 is so formed as to surround the periphery of the anodeelectrodes 211 (211 _(R), 211 _(G), 211 _(B)) formed on a pixel-by-pixelbasis, specifically at the same layer as that of the anode electrodes211.

Furthermore, to this metal interconnect 90, a potential lower than thepotential of the anode electrode 211 in the non-light-emission state ofthe white organic EL element 21 _(W), e.g. the potential of the cathodeelectrode 212 (cathode potential V_(cath)), is given. Using the cathodepotential V_(cath) as the potential of the metal interconnect 90provides an advantage that the potential used exclusively for the metalinterconnect 90 does not need to be prepared.

It is preferable to use, as the material of the metal interconnect 90,the same material as that of the anode electrode 211, e.g. aninterconnect material such as aluminum (Al) or silver (Ag). This isbecause using the same material as that of the anode electrode 211 asthe material of the metal interconnect 90 provides an advantage that themetal interconnect 90 can be formed in the same step as that of theanode electrode 211 and thus the number of steps does not need to beincreased. Forming the metal interconnect 90 at the same layer as thatof the anode electrode 211 is also because of the same reason.

A contact hole 71 _(B) is formed at the site between the pixels in thewindow insulating film 71, i.e. the site at which the metal interconnect90 is formed. Via this contact hole 71 _(B), the metal interconnect 90is electrically connected to the organic layer 213, specifically thecharge injection layer 214 as the lowermost layer of the organic layer213 in the present example.

2-2. Operation and Effect of Embodiment

The following operation and effect can be achieved by forming the metalinterconnect 90 electrically connected to the organic layer 213 in sucha manner that the metal interconnect 90 surrounds the periphery of theanode electrode 211 and setting the potential of the metal interconnect90 to the cathode potential V_(cath) as described above. Specifically,when a leakage current flows in the lateral direction through the commonlayer in the organic layer 213, specifically through the chargeinjection layer 214 and the connecting layers 216 and 217 in the presentexample, the leakage current flows into the metal interconnect 90through the site of the contact hole 71 _(B) (hereinafter, referred toas “contact part 71 _(B)”) as shown in FIG. 12.

Thus, the leakage current flowing through the charge injection layer 214completely flows into the metal interconnect 90 because this chargeinjection layer 214 is electrically connected to the metal interconnect90. That is, the leakage current flowing in the lateral directionthrough the charge injection layer 214 is completely blocked fromflowing to the adjacent pixel side by the contact part 71 _(B).

The leakage current flowing in the lateral direction through theconnecting layers 216 and 217 is divided into a component flowing intothe contact part 71 _(B), a component flowing into the adjacent pixelside, and a component contributing to light emission. Therefore, theleakage current flowing through the connecting layers 216 and 217 canalso be reduced compared with the case in which the metal interconnect90 is not provided. In FIG. 12, the size of the arrow representing thelight emission color conceptually indicates the intensity of this light.FIG. 13 shows the equivalent circuit of the display panel having thepixel structure according to the embodiment.

In this manner, the leakage current flowing into the adjacent pixel sidecan be reduced even when the leakage current flows in the lateraldirection through the charge injection layer 214 and the connectinglayers 216 and 217. This can suppress light emission in the adjacentpixel attributed to the leakage current and thus can achieve favorablecolor reproducibility (color purity).

In the present embodiment, the metal interconnect 90 surrounding theperiphery of the anode electrode 211 is formed at the common layer withthe anode electrode 211. However, the configuration is not limitedthereto. Specifically, the layer at which the metal interconnect 90 isformed may be any layer as long as it is a layer that can beelectrically connected to the organic layer 213 of the white organic ELelement 21 _(W).

Furthermore, the potential of the metal interconnect 90 surrounding theperiphery of the anode electrode 211 is set to the cathode potentialV_(cath) in the present embodiment. However, the potential is notlimited to the cathode potential V_(cath) but may be any potential aslong as it is a potential lower than the potential of the anodeelectrode 211 in the non-light-emission state of the white organic ELelement 21 _(W).

3. Modification Example

The above-described embodiment is explained by taking as an example thecase of employing the system in which the respective color light beamsof RGB are obtained by the combination of the white organic EL element21 _(W) and the color filter 80 and applying the system to the pixelstructure (display panel) of the tandem structure. However, the presentdisclosure is not limited to this application example. Specifically,embodiments of the present disclosure can be applied to the overallorganic EL display devices that do not employ the configuration of thetandem structure but have a pixel structure including at least onecommon layer formed in an organic layer in common to the pixels.

However, in the case of the pixel structure of the tandem structure, theconnecting layers 216 and 217 to couple the light emitting unitsincluding the light emitting elements of the respective color lightbeams exist and a leakage current flows through these connecting layers216 and 217. Thus, the problem associated with the leakage current issignificant. Therefore, it can be said that the advantageous effects ofthe technique of the present disclosure are extremely large when anembodiment of the present disclosure is applied to the pixel structureof the tandem structure particularly.

Examples of other pixel structures including at least one common layerin an organic layer include a pixel structure employing the RGB maskseparate-application system, in which organic EL materials of RGB areseparately applied by evaporation with use of a mask. This pixelstructure will be described with use of FIG. 14.

Referring to FIG. 14, the charge injection layer 214 is formed as acommon layer on the anode electrodes 211 _(R), 211 _(G), and 211 _(B)formed on a pixel-by-pixel basis and the window insulating film 71, andorganic EL elements 21 _(R), 21 _(G), and 21 _(B) of R, G, and B areformed on the charge injection layer 214. Furthermore, the cathodeelectrode 212 is formed on the organic EL elements 21 _(R), 21 _(G), and21 _(B) in common to all pixels, and the color filter 80 is formed in anon-chip form over the cathode electrode 212 with the intermediary of theinterlayer insulating film 72.

In the case of the pixel structure employing the RGB maskseparate-application system, the organic EL elements 21 _(R), 21 _(G),and 21 _(B) of R, G, and B themselves emit the respective color lightbeams. Therefore, originally the color filter 80 is unnecessary.However, using the color filter 80 in combination provides an advantagethat the color purity can be enhanced.

Also in the pixel structure employing the above-described RGB maskseparate-application system, because of the existence of a common layercommon to the pixels, specifically the charge injection layer 214 in thepresent example, the occurrence of the problem associated with a leakagecurrent flowing into an adjacent pixel through this charge injectionlayer 214 is inevitable. Therefore, the above-described embodiment canbe similarly applied also to a pixel structure that employs the RGB maskseparate-application system and has a common layer among the pixels.

Specifically, in the pixel structure employing the RGB maskseparate-application system shown in FIG. 14, a metal interconnectelectrically connected to the organic layer (charge injection layer 214)is so formed as to surround the periphery of the anode electrodes 211_(R), 211 _(G), and 211 _(B). In addition, the potential of this metalinterconnect is set to a potential lower than the potentials of theanode electrodes 211 _(R), 211 _(G), and 211 _(B) in thenon-light-emission state of the organic EL elements 21 _(R), 21 _(G),and 21 _(B). Thereby, operation and effect similar to those of theabove-described embodiment can be achieved.

4. Electronic Apparatus

The organic EL display device according to the above-describedembodiment of the present disclosure can be applied to a display section(display device) of electronic apparatus in every field that displays avideo signal input to the electronic apparatus or a video signalgenerated in the electronic apparatus as image or video. As one example,embodiments of the present disclosure can be applied to display sectionsof various pieces of electronic apparatus shown in FIG. 15 to FIG. 19G,specifically e.g. digital camera, notebook personal computer, portableterminal device such as a cellular phone, and video camcorder.

By using the organic EL display device according to one embodiment ofthe present disclosure as the display section of electronic apparatus inevery field in this manner, the display quality of various kinds ofelectronic apparatus can be enhanced. Specifically, as is apparent fromthe explanation of the above-described embodiment, the organic ELdisplay device according to one embodiment of the present disclosure cansuppress light emission in an adjacent pixel even when a leakage currentflows in the lateral direction through a common layer in an organiclayer, and thus can achieve favorable color reproducibility (colorpurity). As a result, favorable displayed images having high quality canbe achieved in various kinds of electronic apparatus.

The display device according to one embodiment of the present disclosureincludes also a display device having a module shape based on a sealedconfiguration. As one example, a display module formed by applying anopposed section such as transparent glass to a pixel array sectioncorresponds to such a display device. The display module may be providedwith a circuit section, a flexible printed circuit (FPC), etc. forinput/output of a signal and so forth from the external to the pixelarray section.

Specific examples of the electronic apparatus to which one embodiment ofthe present disclosure is applied will be described below.

FIG. 15 is a perspective view showing the appearance of a television setto which one embodiment of the present disclosure is applied. Thetelevision set according to the present application example includes avideo display screen section 101 composed of a front panel 102, a filterglass 103, etc. and is fabricated by using the organic EL display deviceaccording to one embodiment of the present disclosure as the videodisplay screen section 101.

FIG. 16 is a perspective view showing the appearance of a digital camerato which one embodiment of the present disclosure is applied. FIG. 16Ais a perspective view of the front side and FIG. 16B is a perspectiveview of the back side. The digital camera according to the presentapplication example includes a light emitter 111 for flash, a displaysection 112, a menu switch 113, a shutter button 114, etc. and isfabricated by using the organic EL display device according to oneembodiment of the present disclosure as the display section 112.

FIG. 17 is a perspective view showing the appearance of a notebookpersonal computer to which one embodiment of the present disclosure isapplied. The notebook personal computer according to the presentapplication example includes, in its main body 121, a keyboard 122operated when characters and so forth are input, a display section 123that displays images, etc. and is fabricated by using the organic ELdisplay device according to one embodiment of the present disclosure asthe display section 123.

FIG. 18 is a perspective view showing the appearance of a videocamcorder to which one embodiment of the present disclosure is applied.The video camcorder according to the present application exampleincludes a main body section 131, a lens 132 that exists on the frontside and is used for subject photographing, a start/stop switch 133operated in photographing, a display section 134, etc. and is fabricatedby using the organic EL display device according to one embodiment ofthe present disclosure as the display section 134.

FIGS. 19A to 19G are appearance diagrams showing a cellular phone as anexample of a portable terminal device to which one embodiment of thepresent disclosure is applied: FIG. 19A is a front view of the openedstate, FIG. 19B is a side view of the opened state, FIG. 19C is a frontview of the closed state, FIG. 19D is a left side view, FIG. 19E is aright side view, FIG. 19F is a top view, and FIG. 19G is a bottom view.The cellular phone according to the present application example includesan upper chassis 141, a lower chassis 142, a connecting part (in thisexample, hinge part) 143, a display 144, a sub-display 145, a picturelight 146, a camera 147, etc. The cellular phone according to thepresent application example is fabricated by using the organic ELdisplay device according to one embodiment of the present disclosure asthe display 144 and the sub-display 145.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2011-013049 filed in theJapan Patent Office on Jan. 25, 2011, the entire content of which ishereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors in so far as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An organic electroluminescence display devicecomprising: a plurality of anode electrodes arranged in a matrix; aphysically-unitary common layer having a plurality of light emissionregions respectively corresponding to each of the anode electrodes, thephysically-unitary common layer being formed on the anode electrodes andincluding at least one constituent-layer made of an organic material; adriving circuitry configured to selectively provide driving current tothe anode electrodes such that each of the light emission regionsselectively emits light; a metal interconnect directly electricallyconnected to the physically-unitary common layer; a common cathodeelectrode formed on the physically-unitary common layer, wherein thedriving circuitry is configured to: apply a first potential to thecommon cathode electrode, and apply a second potential to the metalinterconnect, where the second potential is set such that, when thesecond potential is applied to the anode electrode corresponding to agiven one of the light emission regions and the first potential isapplied to the common cathode electrode, the given one of the lightemission regions does not emit light.
 2. The display device according toclaim 1, wherein the metal interconnect is disposed between two of theanode electrodes.
 3. The display device according to claim 1, whereinthe metal interconnect is disposed so as to surround each of the anodeelectrodes.
 4. The display device according to claim 1, wherein themetal interconnect is disposed on a same layer as the anode electrodes.5. The display device according to claim 1, wherein theconstituent-layer is a light emission layer and each of the lightemission regions is configured to emit light of substantially the samecolor as one another.
 6. The display device according to claim 5,further comprising a plurality of color filters respectively disposed soas to correspond to each of the light emission regions.
 7. The displaydevice according to claim 1, wherein the physically-unitary common layerincludes a plurality of light emission layers stacked in a thicknessdirection, respectively configured to emit light of different colors. 8.The display device according to claim 7, wherein the physically-unitarycommon layer further includes an intermediate conductive layer disposedbetween the light emission layers.
 9. An organic electroluminescencedisplay device comprising: a plurality of pixel electrodes, a commonorganic layer continuously formed on the pixel electrodes, the commonorganic layer having a plurality of light emission regions configured toselectively emit light of substantially the same color as one another,each of the emission regions respectively corresponding to each of thepixel electrodes, a conductive layer formed on the common organic layer;a driving circuitry configured to drive each of the pixel electrodes;and a metal interconnect directly electrically connected to the commonorganic layer.
 10. The display device according to claim 9, furthercomprising a plurality of color filters respectively disposed so as tocorrespond to each of the light emission regions.
 11. The display deviceaccording to claim 9, wherein the common organic layer includes aplurality of light emission layers stacked in a thickness direction,respectively configured to emit light of different colors.
 12. Thedisplay device according to claim 11, wherein the common organic layerfurther includes an intermediate conductive layer disposed between thelight emission layers.
 13. The display device according to claim 9,wherein the metal interconnect is disposed between two of the pixelelectrodes.
 14. An organic electroluminescence electronic apparatuscomprising: a plurality of first electrodes; a physically-unitary commonlayer having a plurality of light emission regions respectivelycorresponding to each of the first electrodes, the physically-unitarycommon layer being formed on the first electrodes and including at leastone constituent-layer made of an organic material; a driving circuitryconfigured to selectively provide driving current to the firstelectrodes such that each of the light emission regions emits light; ametal interconnect directly electrically connected to thephysically-unitary common layer; a second electrode formed commonly onthe physically-unitary common layer, wherein the driving circuitry isconfigured to: apply a first potential to the common cathode electrode,and apply a second potential to the metal interconnect, where the secondpotential is set such that, when the second potential is applied to thefirst electrode corresponding to a given one of the light emissionregions and the first potential is applied to the second electrode, thegiven one of the light emission regions does not emit light.
 15. Theelectronic apparatus according to claim 14, wherein thephysically-unitary common layer includes a plurality of light emissionlayers stacked in a thickness direction, respectively configured to emitlight of different colors.
 16. The electronic apparatus according toclaim 15, wherein the physically-unitary common layer further includesan intermediate conductive layer disposed between the light emissionlayers.
 17. The electronic apparatus according to claim 14, wherein theelectronic apparatus is a device selected from a group consisting of adigital camera, a notebook personal computer, a portable terminal deviceand a video camcorder.
 18. The display device according to claim 15,wherein the driving circuitry is configured to: apply a first potentialto the conductive layer, and apply a second potential to the metalinterconnect, where the second potential is set such that, when thesecond potential is applied to the pixel electrode corresponding to agiven one of the light emission regions and the first potential isapplied to the conductive layer, the given one of the light emissionregions does not emit light.
 19. An organic electroluminescence displaydevice comprising: a plurality of pixel electrodes, a common organiclayer continuously formed on the pixel electrodes, the common organiclayer having a plurality of light emission regions configured toselectively emit light of substantially the same color as one another,each of the emission regions respectively corresponding to each of thepixel electrodes, a conductive layer formed on the common organic layer;a driving circuitry configured to drive each of the pixel electrodes, adrainage electrode disposed in direct contact with the common organiclayer, and configured to absorb charge that is provided from a given oneof the pixel electrodes and is flowing through the common organic layer.20. The display device according to claim 19, wherein the drainageelectrode is configured to prevent a current flowing from the given oneof the pixel electrodes to an adjacent one of the light emission regionsby absorbing the charge.